Motion adaptive de-interlacing method and apparatus

ABSTRACT

A system and method for generating an interpolated pixel at a vertical position in a field of a video frame. The method comprises the steps of receiving at least two pixels vertically adjacent the vertical position in the field and at least three pixels from at least one adjacent field, detecting a degree of motion in the vicinity of the interpolated pixel, providing weighting factors based on the degree of motion, and calculating the interpolated pixel based on a combination of weighted contributions from the at least two pixels and the at least three pixels. The weighted contributions are derived from a combination of the weighting factors and at least vertical-temporal and temporal interpolation. For at least one degree of said motion, the weighted contributions comprise at least (i) a first positive contribution derived from immediately adjacent ones of the at least two pixels, (ii) a second positive contribution derived from a central one of the at least three pixels located at the vertical position, and (iii) a negative contribution derived from the two of the at least three pixels that are immediately vertically adjacent the central pixel.

FIELD OF THE INVENTION

[0001] This invention relates in general to digital video signalprocessing and more particularly to a method and apparatus forde-interlacing video fields to progressive scan video frames usingmotion adaptive techniques.

BACKGROUND OF THE INVENTION

[0002] The NTSC and PAL video standards are in widespread use throughoutthe world today. Both of these standards make use of interlacing inorder to maximize the vertical refresh rate thereby reducing wide areaflicker, while minimizing the bandwidth required for transmission. Withan interlaced video format, half of the lines that make up a picture aredisplayed during one vertical period (e.g. the even field), while theother half are displayed during the next vertical period (e.g. the oddfield) and are positioned halfway between the lines displayed during thefirst period. While this technique has the benefits described above, theuse of interlacing can also lead to the appearance of artifacts such asline flicker and visible line structure.

[0003] It is well known in the prior art that the appearance of aninterlaced image can be improved by converting it to non-interlaced(progressive) format and displaying it as such. Moreover, many newerdisplay technologies, for example Liquid Crystal Displays (LCDs), arenon-interlaced by nature, therefore conversion from interlaced toprogressive format is necessary before an image can be displayed at all.

[0004] Numerous methods have been proposed for converting an interlacedvideo signal to progressive format. For example, linear methods havebeen used whereby missing pixels in the progressive output sequence aregenerated as a linear combination of spatially and/or temporallyneighbouring pixels from the interlaced input sequence, such asdescribed in U.S. Pat. No. 6,266,092 (Wang). Although this approach mayproduce acceptable results under certain conditions, the performancegenerally represents a trade off between vertical spatial resolution andmotion artifacts. Rather than accept this compromise, it is possible toachieve enhanced performance by employing a method that is capable ofadapting to the type of source material. For instance, it is well knownthat conversion from interlaced to progressive format can beaccomplished with high quality for sources that originate from motionpicture film or from computer graphics (CG). Such sources are inherentlyprogressive in nature, but are transmitted in interlaced format inaccordance with existing video standards. For example, motion picturefilm created at 24 frames per second is converted to interlaced video at60 fields per second using a process known as 3:2 pull down, where 3fields are derived from one frame and 2 are derived from the next, so asto provide the correct conversion ratio. Similarly, a computer graphicssequence created at 30 frames per second is converted to interlacedvideo at 60 fields per second using a pull down ratio of 2:2, where 2fields are derived from each CG frame. By recognizing that a videosequence originates from a progressive source, it is possible for aformat converter to reconstruct the sequence in progressive formatexactly as it was before the conversion to interlaced format.

[0005] For video that is not derived from a progressive source, thereare other alternatives to linear processing. For instance, U.S. Pat. No.4,989,090 (Campbell) describes one approach to a technique generallyreferred to as motion adaptive de-interlacing. In this method, missingpixels are generated in one of two different ways depending on whethermotion is detected in the vicinity of the missing pixel. If little or nomotion is detected, then the missing pixel is derived primarily from itstemporal neighbours, thereby giving the best vertical resolution forstatic portions of the image. If a higher amount of motion is detected,then the missing pixel is derived primarily from its verticalneighbours, thereby avoiding motion artifacts, albeit at the expense ofvertical resolution. Depending on the degree of motion detected, themissing pixel may be derived using a greater or lesser contribution fromits temporal neighbours and vertical neighbours. This technique is usedtoday in numerous consumer electronic systems. It should be noted that,in this specification, the term “degree of motion” includes the absenceof motion.

[0006] In order to achieve adequate performance in the above system, itis necessary for the system to derive the missing pixel from itsvertical neighbors even when only very small amounts of motion aredetected. This is necessary to avoid motion artifacts commonly referredto as “feathering” which result when pixels from different fields areerroneously combined in the presence of motion. Since the resultobtained when interpolating between vertical neighbours, as in themotion case, may be quite different from that obtained when using thetemporal neighbours, as in the static case, certain artifacts may beproduced as a result of a transition between the two cases. Theartifacts are a result of the property that a small change in anotherwise static portion of the image may produce a much larger changeat the output. Consequently, noise may be amplified and vertical detailmay tend to scintillate in the presence of subtle motion. Theseartifacts are inherent in such systems and may be reduced but notcompletely eliminated.

[0007] The preceding problem may be partially alleviated bytransitioning smoothly between the motion and static cases with varyingdegrees depending on the level of motion detected. In order to avoid thefeathering artifacts described above, experimental observation has shownthat the initial transition towards the motion case must begin for smallamounts of motion (in the range of 2-3% of full scale value) and thatfull transition to the motion case must occur shortly thereafter (in therange of 5-10% of fall scale value). Therefore, the function thatrelates the weightings of the static and motion cases to the measuredmotion value will have high gain in the transition region. Hence, thesystem will, to a large degree, still possess the property that a smallchange at the input may produce a much larger change at the output. Thisis a property which, as described earlier, can lead to noise andscintillation artifacts. It is an objective of the present invention toprovide a method to alleviate the problems associated with the criticaltransition region of motion adaptive de-interlacers.

[0008] The following patents are relevant as prior art relative to thepresent invention: U.S. Patent Documents 4,989,090-Campbell Jan. 29,1991 Television Scan Line Doubler Including Temporal Median Filter4,967,271-Campbell Oct. 30, 1990 Television Scan Line Doubler IncludingTemporal Median Filter 4,789,893-Weston Dec. 6, 1988 Interpolating Linesof Video Signals 6,266,092-Wang Jul. 24, 2001 Method and Apparatus forVideo Line Multiplication with Enhanced Sharpness

SUMMARY OF THE INVENTION

[0009] According to the present invention, a method and apparatus areprovided for motion adaptive de-interlacing of interlaced signals withgreater immunity to noise and scintillation artifacts than is commonlyassociated with prior art solutions. In the present invention, verticalinterpolation, which the prior art employs in the presence of motion, isreplaced by a two-dimensional, non-separable, vertical-temporalinterpolation filter with specific frequency characteristics. Thevertical-temporal filter is designed such that for static imageportions, the contribution from the current field (the field for whichthe missing pixel is being derived) is enhanced by a contribution fromone or more adjacent fields so as to provide an estimate for the missingpixel which is a better approximation to that which would have beencalculated using temporal interpolation as normally employed in theabsence of motion. The fact that the estimate for the missing pixel willbe similar for static portions of the image regardless of whethervertical-temporal or temporal interpolation is used, reduces theartifacts associated with the transition between the two processingmodes. Furthermore, the vertical-temporal filter is designed such thatfeathering artifacts in moving portions of the image are avoided.

[0010] Although vertical-temporal interpolation outperforms verticalinterpolation for static portions of an image, vertical interpolation isgenerally better than vertical-temporal interpolation for areas of highmotion, since the adjacent field component associated with the lattercomes from an area of the image that may be uncorrelated to the currentfield component. Thus it may not be obvious to a person of ordinaryskill in the art that vertical-temporal interpolation would be preferredover vertical interpolation in the presence of motion, as provided bythe method of the present invention. However, the benefit of thisapproach derives from the fact that there is a finite range ofvelocities for which vertical-temporal interpolation offers an advantageover vertical interpolation. Since the transition between the static andmotion modes needs to occur even for small amounts of motion,vertical-temporal interpolation is utilized in cases where it offers anadvantage. The lesser performance of vertical-temporal interpolation athigher levels of motion is generally acceptable to the human eye.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A description of the prior art and of the preferred embodiment ofthe present invention are provided hereinbelow with reference to thefollowing drawings in which:

[0012]FIG. 1 is a schematic representation showing how a missing pixelmay be generated using a combination of vertical and temporalinterpolation depending on the presence of motion, according to theprior art.

[0013]FIG. 2 is a numerical example of temporal interpolation, accordingto the prior art.

[0014]FIG. 3 is a schematic representation showing how a missing pixelmay be generated using vertical interpolation, according to the priorart.

[0015]FIG. 4 is a numerical example of vertical interpolation, accordingto the prior art.

[0016]FIG. 5 and FIG. 6 are graphical representations of the example ofFIG. 4.

[0017]FIG. 7 is a schematic representation showing how a missing pixelmay be generated using a combination of vertical-temporal and temporalinterpolation depending on the presence of motion, according to themethod of the present invention.

[0018]FIG. 8 is a schematic representation showing how a missing pixelmay be generated using vertical-temporal interpolation, according to themethod of the present invention.

[0019]FIG. 9 is a numerical example of vertical-temporal interpolation,according to the method of the present invention.

[0020]FIG. 10 and FIG. 11 are graphical representations of the exampleof FIG. 9.

[0021]FIG. 12 is a numerical example of vertical interpolation in thepresence of vertical motion.

[0022]FIG. 13 is a numerical example of vertical-temporal interpolationin the presence of vertical motion.

[0023]FIG. 14 is a graphical representation of the examples of FIG. 12and FIG. 13.

[0024]FIG. 15 is a schematic representation showing how a missing pixelmay be generated using a combination of temporal, vertical-temporal andvertical interpolation, depending on the level of motion.

[0025]FIG. 16 is a block diagram of an apparatus for implementing themethod according to one embodiment of the present invention.

[0026]FIG. 17 is a block diagram of an apparatus according to analternative but equally preferable embodiment for implementing themethod of the present invention and for performing arbitrary verticalscaling.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027]FIG. 1 depicts a method of line doubling similar to that describedin U.S. Pat. No. 4,989,090 (Campbell). According to the illustratedmethod, a missing pixel P is generated using a combination of verticalinterpolation and temporal interpolation, depending on the presence ofmotion in the vicinity of P. In the presence of motion, P is derivedprimarily from its vertical neighbours A and B. In the absence ofmotion, P is derived primarily from its temporal neighbours C and D. Itshould be noted that in this example and those that follow, temporalinterpolation means “zero order” interpolation in which the interpolatedpixel is taken as one of either C or D, however, other forms of temporalinterpolation are also possible. Depending on the degree of motiondetected, a weighting function ALPHA is used to control the contributiontaken from the vertical and temporal neighbours of P. In order to avoidfeathering artifacts, the relationship between ALPHA and the degree ofmotion detected must be approximately as shown in the plot at the rightof FIG. 1. This plot shows a steep transition from the static casetowards the motion case in the presence of small amounts of motion.

[0028]FIG. 2 shows how the method of FIG. 1 produces the desired effectin the absence of any motion. The left half of the figure shows an inputsequence of interlaced fields and the right half shows the resultingline doubled output sequence. In both diagrams, the vertical axisrepresents the vertical position of each line within the image and thehorizontal axis represents the sequence of fields/frames in time. Thehorizontal dimension of the image is normal to the page such that eachpoint in the diagram represents an entire line of pixels viewededgewise. Each field in the input sequence contains a single “1” whilethe rest of the field contains “0”. This is representative of a singlehorizontal white line on a black background and is commonly known as animpulse. Since the “1” is present at the same location in fields of thesame parity, no motion is detected and the method of FIG. 1 will degradeto purely temporal interpolation. The resulting line doubled sequencewill contain two “1's” in each output frame and all output frames willbe identical which is the desired result for an image that contains nomotion.

[0029] Now let us assume that a small change in the input sequence dueto either noise or the onset of motion causes the system of FIG. 1 totransition to the motion case. In the presence of motion, the missingpixel P is calculated using vertical interpolation which as shown inFIG. 3 can be performed simply by taking the average of the two closestvertical neighbours, A and B. FIG. 4 shows the impulse response to thesame input sequence as in FIG. 2 only this time using verticalinterpolation corresponding to the motion case. The noise and/or onsetof motion that caused the transition to the motion case is not reflectedin the data values of FIG. 4 since it is assumed to be small and tosimplify the example. Note the periodic nature of the line doubledoutput sequence despite the fact that the input is essentially static.

[0030]FIG. 5 shows a graphical representation of the example of FIG. 4.The two lines represent the impulse response for each field whenvertical interpolation is used. A distinct offset will be noted betweenthe response for each field which suggests that the apparent position ofeach pulse as perceived by the viewer will change from one field to thenext. Indeed, on display devices with fast response times such as CRTs,the line will appear to flicker despite the use of progressive scanning.

[0031] Since the eye acts as an integrator, the viewer will tend toperceive the overall sharpness of the impulse based on the average ofthe two frames. FIG. 6 shows a graphical representation of the frameaveraged impulse of the example of FIG. 4. The rounder flatterappearance of this impulse is characteristic of a loss of sharpnessperceived by the viewer. Moreover, the sudden change in appearanceassociated with the onset of motion from the pristinely reproducedimpulse provided by temporal interpolation, to the poorly reproducedimpulse provided by vertical interpolation, is most problematic. It isthis phenomenon which may result in the amplification of noise and theappearance of scintillation artifacts commonly associated with motionadaptive line doublers.

[0032]FIG. 7 shows a first embodiment of the method of the presentinvention. In the illustrated method, the missing pixel P is generatedfrom neighbouring pixels depending on the degree of motion detected inthe vicinity of P. In the absence of motion, P is generated usingtemporal interpolation as in prior art methods, which may also include“zero order” temporal interpolation. In the presence of motion, ratherthan resorting to vertical interpolation as in the prior art,non-separable vertical-temporal interpolation is used to provide animproved impulse response for static and slowly moving image portions,thereby easing the difficulties associated with the critical onset ofmotion.

[0033]FIG. 8 shows a schematic representation of how a missing pixel ata vertical position may be generated using vertical-temporalinterpolation according to one embodiment of the present invention. Themissing pixel P derives a major contribution from the current field,that is the field from which P is considered to be missing. In thisexample, the current field contribution is exactly equal to what itwould have been if pure vertical interpolation had been used, as shownin FIG. 3. P derives a further contribution from an adjacent field whichis used to enhance the impulse response for static and slowly movingimage portions while avoiding feathering artifacts. A vertical-temporalfilter derives contributions from at least two pixels verticallyadjacent the vertical position in the current field and at least threepixels from one or more adjacent fields. A first positive contributionis derived from immediately adjacent ones of the at least two pixels inthe current field. A second positive contribution is derived from acentral one of the at least three pixels in the vertical position of themissing pixel and a negative contribution is derived from the two of theat least three pixels that are immediately adjacent the central pixel.The specific coefficients for one embodiment are shown in FIG. 8. Itshould be noted that there are many other variations within the sphereand scope of the invention, such as increasing the number of taps in anyor all of the fields, or increasing the number of adjacent fields fromwhich a contribution is derived. Additionally, a vertical-temporalinterpolator with a boosted high temporal frequency characteristic maybe used, as disclosed in U.S. Pat. No. 6,266,092 (Wang).

[0034]FIG. 9 shows the impulse response to the same input sequence as inFIG. 4 but using vertical-temporal interpolation as provided by thepresent invention. The noise and/or onset of motion that caused thetransition to the motion case is not reflected in the data values ofFIG. 9 since it is assumed to be small. It should be noted that the linedoubled output sequence still contains a periodic component but to amuch lesser degree than that associated with simple verticalinterpolation as shown in FIG. 4.

[0035]FIG. 10 shows a graphical representation of the example of FIG. 9.The two lines represent the impulse response for each field whenvertical-temporal interpolation is used. It should be noted that thereis only a slight difference between the response for each field ascompared with vertical interpolation indicating that flicker issignificantly reduced through the use of vertical-temporalinterpolation. Similarly, the frame averaged impulse as shown in FIG. 11is much sharper than that of FIG. 6, indicating that the sharpnessperceived by the viewer will also be improved. Moreover, the change inappearance of an image detail owing to the onset of motion issignificantly reduced as compared to vertical interpolation. Thus, theamplification of noise and the appearance of scintillation artifactscommonly associated with motion adaptive de-interlacers is effectivelyavoided.

[0036]FIG. 12 shows the response of the vertical interpolator of FIG. 3to an impulse moving vertically downward at a velocity of 1 line/fieldas referred to the input field resolution. The reproduction of theimpulse in each output frame is essentially the same as it would be fora static impulse, since vertical interpolation does not depend onneighbouring fields (the only slight difference in this example is dueto a difference in the input impulse itself). If the observer's eyetracks the motion of the impulse, the frame average perceived by theviewer will be the average of successive frames which are shifted inaccordance with the optical flow. The trajectory along which frameaveraging occurs during eye tracking is indicated by the arrow.

[0037] The response of the inventive vertical-temporal interpolator ofFIG. 7 to the moving impulse is shown in FIG. 13. Graphicalrepresentations of the frame averaged vertical and vertical-temporalresponses to the moving impulse with eye tracking are shown in FIG. 14.

[0038] The frame averaged impulse response of the vertical interpolatorof FIG. 3 is essentially unchanged from the response to the static case(when processed using vertical interpolation). The response of theinventive vertical-temporal interpolator of FIG. 7, however, is lesssharp compared to that of the vertical interpolator as shown by theflatter impulse response. Thus, the use of vertical-temporalinterpolation at higher vertical velocities suffers slightly in terms ofimpulse response relative to prior art vertical interpolators. Onbalance, however, this slight reduction represents a reasonable tradeoff since vertical motion is frequently within the range of velocitywhere vertical-temporal interpolation still adds value.

[0039] In another embodiment of the present invention, it is possible toexploit the benefits of vertical-temporal interpolation at the onset ofmotion, while avoiding its pitfalls for higher motion, by blendingbetween vertical-temporal and vertical interpolation, as well asblending between temporal and vertical-temporal interpolation. Referringto FIG. 15, in the absence of motion missing pixels are generated usingonly temporal interpolation. At the onset of motion, missing pixels aregenerated using a weighted combination of temporal and vertical-temporalinterpolation, with an increase in the weighting of thevertical-temporal component for increasing motion. As motion increasesfurther, missing pixels are generated using a weighted combination ofvertical-temporal and vertical interpolation, with an increase in theweighting of the vertical component for higher levels of motion. Thus,the benefits of vertical-temporal interpolation are exploited for lowmotion while the benefits of pure vertical interpolation are exploitedfor high motion.

[0040] The benefits derived from the above-described technique dependsomewhat on the method of motion detection used. Although the presentinvention is not limited to use with any particular method of motiondetection, one of the simplest and preferred methods is based on findingthe absolute difference between similarly located pixels in successiveinput fields. While the advantage of vertical-temporal interpolationover vertical interpolation is greatest over a finite range ofvelocities, the above method of measuring motion does not produce adirect measure of the actual velocity as might be desirable. Forinstance, a sharp edge with high contrast moving at low velocity maystill produce a large difference between similarly located pixels insuccessive frames, which would be interpreted as high motion. Even so,some correlation does exist between actual velocity and the measure ofmotion provided by the absolute difference method of FIG. 15 is ofvalue.

[0041] It should be noted that it is not necessary to adhere strictly tothe weighting schemes in any of the preceding examples. An arbitrarytwo-dimensional, non-separable, vertical-temporal interpolation filterwhose response is altered according to the level of motion, may also beused to advantage.

[0042] The weightings referred to in the preceding examples may beapplied in more than one way with similar results. For instance,separate estimates based on pure temporal and vertical-temporalinterpolation may be derived first with appropriate weighting factorssubsequently applied to provide separate weighted estimates. Theweighted estimates are summed in order to generate the final result.Alternatively, the separate estimates can include an estimate based onvertical interpolation in addition to the pure temporal andvertical-temporal interpolation. Also, the weighting factors may bealready “built in” to the coefficients associated with each of theneighbouring pixels from which a contribution is derived, such that thecoefficients already include a predetermined level of motion weighting.In the latter case, the pre-weighted coefficients may be eithergenerated dynamically based on the weighting factor, or selected fromamong multiple sets of pre-calculated coefficients.

[0043] One embodiment of the method of the present invention can beimplemented using an arrangement of storage elements, coefficient ROMs,and arithmetic elements as shown in FIG. 16. Specifically, a methodsimilar to that shown in FIG. 7, however, not including weightedcontribution from the line labeled C and including two additional linesproviding weighted contributions, one line above the line labeled A andone line below the line labeled B, can be implemented using theapparatus shown in FIG. 16. As each field of an interlaced video signal1 arrives at the input to a memory controller 2, it is written into amemory 3. Concurrently with the operation of writing data into memory,data from the previous field is retrieved from memory and applied to theinput of line store element 6 and multiplier 19 while data from the mostrecently received field is routed through the memory controller andapplied to the input of line store element 4 and multiplier 16. In analternative mode of operation, data from the most recently receivedfield may be retrieved from memory and applied to the input of linestore element 4 and multiplier 16 rather than being routed directlythrough the memory controller. As new data is stored in line store 4,the previously stored data is output and applied to the input of linestore 5 where it replaces the previously stored data. In a similarfashion, the data in line store 6 replaces the data in line store 7which replaces the data in line store 8. Data which is placed into anyline store remains for one input line period which is equal to twooutput line periods before it is replaced with new data. A motiondetector 32 generates a motion signal that is used in conjunction with aselector signal S to address coefficient ROMs 25-31. During one outputline period, the selector signal S causes coefficient ROMs 25-31 todrive out a first set of coefficients that are selected based on thedegree of motion detected by the motion detector 32. The first set ofcoefficients are used to generate the interpolated missing lines. Duringthe next output line period, the selector signal causes an alternate setof coefficients to be driven out, which are used to modify the existinglines (if necessary, depending on the interpolation filter design). Theselector signal S is generated by a controller (not shown) in a wellknown manner. The selected coefficients which appear at the outputs ofcoefficient ROMs 25-31 are applied to one of the inputs of each ofmultipliers 16-22, respectively. The other input of each multiplier 17,18 and 20-22 is driven by the outputs of line stores 4-8, respectively.When the outputs from multipliers 16-22 are summed together using adder23, the output 24 is the desired progressively scanned video signal.

[0044] A person of ordinary skill in the art will appreciate that theweighting coefficients may be generated by circuitry on-the-fly, ratherthan being predetermined and stored in ROMs. Rather than selecting fromamong predetermined weighting coefficients based on the degree ofmotion, weighting coefficients can be generated dynamically usingcoefficients based on vertical-temporal and temporal interpolation,independent of degree of motion. These coefficients are then multipliedby factors (alpha and 1-alpha, respectively) based on the degree ofmotion and then corresponding coefficient components are added togetherto produce the dynamically generated weighting coefficients. It willalso be appreciated that the apparatus described above need not includethe line stores as described. With sufficient bandwidth, all of thelines may be concurrently retrieved from the memory 3 through the memorycontroller 2 rather than being passed consecutively through the linestores using, for example, FIFOs for simultaneously providing multiplestreams of pixel data to the inputs of multipliers 16-22.

[0045] The foregoing description of a preferred embodiment of the systemof the present invention is not restricted to the specific best mode setforth herein. Indeed, the flexible nature of software programming issuch that the broad concepts of the invention may be implemented usingsoftware rather than hardware as set forth herein. Also, as indicatedabove, the principles of the invention are not limited to the specificcase of line doubling. An obvious extension of this method would be tocombine the method of the present invention with additional operationssuch as scaling in order to produce a greater or lesser number of lines.Furthermore, such scaling may include scaling by a non-integer multipleand could either be implemented using a separate processing stage orcould be combined with the method of the present invention andimplemented using a single composite structure. In the latter case, thecoefficients may be split into a number of phases corresponding to anequal number of spatial regions which fall between the input videolines. When an output line must be generated which falls within a givenspatial region, the coefficient set which corresponds to that phase isselected. FIG. 17 shows an apparatus for implementing the above methodin which coefficients are split into phases to enable interpolation atarbitrary positions. The apparatus is similar to that shown in FIG. 16except that the selector signal S has been replaced by a phase selectorbus connected to a scaler control circuit 33 and the address space ofthe coefficient ROMs 25-31 has been increased accordingly. All of thephases for each filter tap are stored within its associated coefficientROM. Depending on the desired spatial position of the output video line,the phase selector signal which is generated by the scaler controlcircuit 33 in a well known manner, is used to address the appropriateset of coefficients.

[0046] It will be appreciated that the present invention can also beused to produce an interlaced video signal of a format that differs fromthat which is inputted. For example, the present invention may be usedto advantage to effect conversion from 480I (standard definitioninterlaced format with 240 active lines per field and a total of 480lines per frame) to 1080I (high definition interlaced format with 540active lines per field and a total of 1080 lines per frame). Regardlessof whether an odd or even field is to be outputted, a required outputline can be mapped to a corresponding position relative to the inputlines. As described above for the progressive output case, when anoutput line must be generated which falls within a given spatial region,the coefficient set which corresponds to that phase is selected.

[0047] A person understanding the present invention may conceive ofother embodiments and variations thereof without departing from thesphere and scope of the invention as defined by the claims appendedhereto.

We claim:
 1. A method for generating an interpolated pixel at a verticalposition in a field of a video frame, comprising: receiving at least twopixels vertically adjacent said vertical position in said field and atleast three pixels from at least one adjacent field; detecting a degreeof motion in the vicinity of said interpolated pixel; providingweighting factors based on said degree of motion; and calculating saidinterpolated pixel based on a combination of weighted contributions fromsaid at least two pixels and said at least three pixels, said weightedcontributions being derived from a combination of said weighting factorsand at least vertical-temporal and temporal interpolation, wherein forat least one degree of said motion said weighted contributions compriseat least (i) a first positive contribution derived from immediatelyadjacent ones of said at least two pixels, (ii) a second positivecontribution derived from a central one of said at least three pixelslocated at said vertical position, and (iii) a negative contributionderived from the two of said at least three pixels that are immediatelyvertically adjacent said central pixel.
 2. The method for generating aninterpolated video pixel according to claim 1, further comprising thestep of providing a plurality of coefficients prior to the step ofcalculating said interpolated pixel and wherein the step of calculatingincludes: selecting respective coefficients from said plurality ofcoefficients for each of said pixels, based on said weighting factorsand said at least vertical-temporal and temporal interpolation;multiplying said at least two pixels and said at least three pixels bysaid respective coefficients in order to produce said weightedcontributions; and summing said weighted contributions.
 3. The methodfor generating an interpolated video pixel according to claim 1, furthercomprising the step of providing a plurality of coefficients prior tothe step of calculating said interpolated pixel and wherein the step ofcalculating includes multiplying said coefficients by said weightingfactors based on said degree of motion to provide a plurality ofresulting products; adding together ones of the resulting products toprovide weighting coefficients based on said degree of motion;multiplying said weighting coefficients by said at least two pixels andsaid at least three pixels to produce said weighted contributions andsumming said weighted contributions.
 4. The method for generating aninterpolated video pixel according to claim 1, wherein the step ofcalculating said interpolated pixel comprises: performing at leastvertical-temporal interpolation and temporal interpolation using said atleast two and said at least three pixels to provide at least first andsecond estimates, respectively, based on contributions from said atleast two pixels and said at least three pixels; multiplying saidestimates by said weighting factors to provide said weightedcontributions; and summing said weighted contributions.
 5. The methodfor generating an interpolated video pixel according to claim 2 whereinthe selected coefficients associated with said at least two pixels sumsubstantially to one, in the presence of motion.
 6. The method forgenerating an interpolated video pixel according to claim 3 wherein theweighting coefficients associated with said at least two pixels sumsubstantially to one, in the presence of motion.
 7. The method forgenerating an interpolated video pixel according to claim 2 wherein theselected coefficients associated with said at least three pixels sumsubstantially to one, in the absence of motion.
 8. The method forgenerating an interpolated video pixel according to claim 3 wherein theweighting coefficients associated with said at least three pixels sumsubstantially to one, in the absence of motion.
 9. The method forgenerating an interpolated video pixel according to claim 1 wherein saidfirst positive contribution increases with increasing degree of motion.10. The method for generating an interpolated pixel according to claim 1wherein said interpolated video pixel forms part of a progressivelyscanned output frame.
 11. The method for generating an interpolatedpixel according to claim 1 wherein said interpolated pixel forms part ofinterlaced output field.
 12. An apparatus for generating an interpolatedpixel at a vertical position in a field of a video frame, comprising:memory for receiving at least two pixels vertically adjacent saidvertical position in said field and at least three pixels from at leastone adjacent field; a motion detector for detecting a degree of motionin the vicinity of said interpolated pixel and for providing weightingfactors based on said degree of motion; and a calculation device forcalculating said interpolated pixel based on a combination of weightedcontributions from said at least two pixels and said at least threepixels, said weighted contributions being derived from a combination ofsaid weighting factors and at least vertical-temporal and temporalinterpolation, wherein said weighted contributions comprise at least (i)a first positive contribution derived from immediately adjacent ones ofsaid at least two pixels, (ii) a second positive contribution derivedfrom a central one of said at least three pixels located in saidvertical position, and (iii) a negative contribution derived from onesof said at least three pixels that are immediately vertically adjacentsaid central pixel.
 13. The apparatus according to claim 12 wherein saidmemory for receiving said at least two pixels and said at least threepixels comprises a plurality of line stores.
 14. The apparatus accordingto claim 13 further comprising a device for providing a plurality ofcoefficients.
 15. The apparatus according claim 14 wherein said devicefor providing a plurality of coefficients comprises a memory forproviding said plurality of coefficients.
 16. The apparatus according toclaim 15 wherein said memory for providing said plurality ofcoefficients comprises a plurality of read-only memory devices.
 17. Theapparatus according claim 14 wherein said calculation device comprises aplurality of multipliers for multiplying said at least two pixels andsaid at least three pixels by said weighting coefficients to providesaid weighted contributions and an adder for summing said weightedcontributions.
 18. The apparatus according to claim 12 wherein saidmemory for receiving said at least two pixels and said at least threepixels comprises a plurality of FIFO units in order to simultaneouslyprovide respective pixels to said multipliers.
 19. The apparatusaccording to claim 12, further comprising a memory controller includingmemory for receiving fields of said video frame and for providing saidpixels to said memory.
 20. A method for generating an interpolated pixelat a vertical position in a field of a video frame, comprising:receiving at least two pixels vertically adjacent said vertical positionin said field and at least three pixels from at least one adjacentfield; detecting a degree of motion in the vicinity of said interpolatedpixel; providing weighting factors based on said degree of motion;providing a plurality of coefficients; selecting respective coefficientsfrom said plurality of coefficients for each of said pixels, based onsaid weighting factors and at least vertical-temporal and temporalinterpolation; multiplying said at least two pixels and said at leastthree pixels by said respective coefficients in order to produce saidweighted contributions; and summing said weighted contributions, whereinfor at least one degree of said motion said weighted contributionscomprise at least (i) a first positive contribution derived fromimmediately adjacent ones of said at least two pixels, (ii) a secondpositive contribution derived from a central one of said at least threepixels located at said vertical position, and (iii) a negativecontribution derived from the two of said at least three pixels that areimmediately vertically adjacent said central pixel.
 21. A method forgenerating an interpolated pixel at a vertical position in a field of avideo frame, comprising: receiving at least two pixels verticallyadjacent said vertical position in said field and at least three pixelsfrom at least one adjacent field; detecting a degree of motion in thevicinity of said interpolated pixel; providing weighting factors basedon said degree of motion; providing a plurality of coefficients;multiplying said coefficients by said weighting factors based on saiddegree of motion to provide a plurality of resulting products; addingtogether ones of the resulting products to provide weightingcoefficients based on said degree of motion; multiplying said weightingcoefficients by said at least two pixels and said at least three pixelsto produce said weighted contributions; and summing said weightedcontributions, wherein for at least one degree of said motion saidweighted contributions comprise at least (i) a first positivecontribution derived from immediately adjacent ones of said at least twopixels, (ii) a second positive contribution derived from a central oneof said at least three pixels located at said vertical position, and(iii) a negative contribution derived from the two of said at leastthree pixels that are immediately vertically adjacent said centralpixel.
 22. A method for generating an interpolated pixel at a verticalposition in a field of a video frame, comprising: receiving at least twopixels vertically adjacent said vertical position in said field and atleast three pixels from at least one adjacent field; detecting a degreeof motion in the vicinity of said interpolated pixel; providingweighting factors based on said degree of motion; performing at leastvertical-temporal interpolation and temporal interpolation using said atleast two and said at least three pixels to provide at least first andsecond estimates, respectively, based on contributions from said atleast two pixels and said at least three pixels; multiplying saidestimates by said weighting factors to provide weighted estimates; andsumming said weighted estimates, wherein for at least one degree of saidmotion the summed weighted estimates comprise at least (i) a firstpositive contribution derived from immediately adjacent ones of said atleast two pixels, (ii) a second positive contribution derived from acentral one of said at least three pixels located at said verticalposition, and (iii) a negative contribution derived from the two of saidat least three pixels that are immediately vertically adjacent saidcentral pixel.